Re: WAL usage calculation patch

On Fri, Mar 6, 2020 at 6:59 PM Kirill Bychik <kirill.bychik@gmail.com> wrote:
>
> пт, 6 мар. 2020 г. в 20:14, Julien Rouhaud <rjuju123@gmail.com>:
> >
> > On Thu, Mar 5, 2020 at 8:55 PM Kirill Bychik <kirill.bychik@gmail.com> wrote:
> > > I wanted to keep the patch small and simple, and fit to practical
> > > needs. This patch is supposed to provide tuning assistance, catching
> > > an io heavy query in commit-bound situation.
> > > Total WAL usage per DB can be assessed rather easily using other means.
> > > Let's get this change into the codebase and then work on connecting
> > > WAL usage to  (auto)vacuum stats.
> >
> > I agree that having a view of the full activity is a way bigger scope,
> > so it could be done later (and at this point in pg14), but I'm still
> > hoping that we can get insight of other backend WAL activity, such as
> > autovacuum, in pg13.
>
> How do you think this information should be exposed? Via the pg_stat_statement?

That's unlikely, since autovacuum won't trigger any hook.  I was
thinking on some new view for pgstats, similarly to the example I
showed previously. The implementation is straightforward, although
pg_stat_database is maybe not the best choice here.

> Anyways, I believe this change could be bigger than FPI. I propose to
> plan a separate patch for it, or even add it to the TODO after the
> core patch of wal usage is merged.

Just in case, if the problem is a lack of time, I'd be happy to help
on that if needed.  Otherwise, I'll definitely not try to block any
progress for the feature as proposed.

> Please expect a new patch version next week, with FPI counters added.

Thanks!